1. Field of the Invention
This invention is directed generally to an improved injection syringe assembly, in particular, a disposable injection syringe assembly.
More particularly, this invention relates to a cannula shield device for an injection syringe, comprising a rear fastening portion provided for attachment to a syringe body and a forward sheath portion integrally connected therewith and separable therefrom, for instance, at a predetermined breaking point.
Furthermore, this invention relates to a cannula module including such a cannula shield device and a cannula received in a cannula holding means within the interior of the cannula shield device.
Also, the invention relates to an injection syringe comprising a syringe body and a cannula module of the above kind as well as, furthermore, a syringe body for such an injection syringe, including a hub for attaching a cannula module.
Finally, this invention is directed to a method of assembling and filling an injection syringe.
2. Description of Related Art
In AT-B-242 286 a cannula shield device comprising a rear fastening portion and a forward sheath portion is disclosed, both portions being connected via a predetermined breaking point. A separate cannula holding means firmly fixed in the cannula shield device is provided for attachment of the cannula. An inner cone is provided in the rear fastening portion for fastening the cannula shield device to a syringe body. However, with this cannula shield device no seal is provided for the cannula; instead, the cannula shield device is used, in particular, with an injection syringe in which a separate ampoule sealed by a membrane is inserted in a cylinder, the membrane being pierced through by a sharpened rear end of the cannula. However, providing a separate ampoule with a membrane as well as a rearwardly protruding sharpened cannula end is relatively expensive.
From U.S. Pat. Nos. 4,735,311, 4,986,818 and 5,085,647, disposable injection syringes are known, with which the cannula is rigidly mounted in a hub of the syringe body and a cannula shield device is placeable over the cannula, said cannula shield device including an internal channel conically narrowed towards the tip of the cannula and merging into a cavity widened in the region of the cannula tip. Into this widened cavity, a rubber plug is introducible into which the cannula tip projects and by which the forward opening of the cannula is tightly closed. The rubber plug, on the side of the cannula, is supported on an abutment surface of the cannula shield device. It is introduced through an opening corresponding to the internal diameter of the cavity and provided on the forward end of the cannula shield device, whereupon this opening is plastically deformed by deforming the forward end of the cannula shield device in a manner that the rubber plug is held in the cannula shield device such that it cannot get lost. Yet, in doing so, an opening remains on the forward end of the cannula shield device towards the cavity receiving the rubber plug. A comparable injection syringe having a cylindrical cannula shield device in which a plug-like cannula seal is inserted is known from DE-C-848 081.
With these known injection syringes, the cannula shield device is simply slipped on the forward end of the cannula-carrying part of the syringe body, optionally latching or snapping over an annularly protruding collar of the cannula-carrying part of the syringe body, for instance, according to U.S. Pat. No. 4,735,311. Hence results the problem that manipulations at the injection syringe will not be noticed; in particular, it will not be recognized whether the cannula shield device has already been removed and the injection syringe has already been used.
A cannula directly glued in the syringe body additionally involves the disadvantage of difficult manufacturing of the injection syringe, because the internal wall of the syringe body, as a rule, must be treated with a lubricant applied by evaporation at a elevated temperature. Yet, the adhesive by which the cannula is glued in the syringe body does not withstand such high temperatures without getting discolored, or destroyed, respectively. On the other hand, it is also difficult to provide a syringe body already treated with lubricant with a cannula, since a lubricant-treated surface no longer takes an adhesive.
The difficulty implied by an adhesive connection for the cannula directly to the syringe body in treating the internal wall of the syringe body with a lubricant, in particular, silicone (what is called "silicone-treating" of the syringe body internal wall), is avoided with the injection syringe according to AT-B-360 139, i.a., by gluing the cannula in a cannula holding means to be placed on a syringe cone of the syringe body afterwards by means of a latch connection. To this end, the syringe body is formed with a peripheral annular groove in which hook- or nose-shaped latch elements provided on the rear slitted end of the cannula holding means engage.
Then, a cannula shield device is slipped on the externally conical cannula holding means.
However, the latch connection for the cannula holding means on the syringe cone involves problems for two reasons: Firstly, the cannula holding means, in respect of the glued-in cannula, is to be comprised of a relatively hard and stiff synthetic material, the latch elements, thus, being subject to relatively easy breaking and, moreover, a tight fit of the cannula holding means on the syringe cone being hardly obtainable, and secondly, the structure of the syringe cone is weakened by the annular groove incorporated therein such that the syringe cone can be broken off relatively easily. Furthermore, cracks may form in the hard plastics material of the cannula holding means, resulting in leakages. Again, the cannula shield device is not secured against unauthorized manipulations, since it is merely slipped on.
U.S. Pat. No. 3,889,673 describes a cannula shield device comprising a separate front cap latched on a sheath member surrounding the cannula. The reason for the cannula shield device being divided in two parts resides in that the syringe is rendered more suitable for various use purposes, wherein, on the one hand, only the front cap of the cannula shield device is removed in order to add a medicament through a nipple to a liquid contained in a bag and, on the other hand, the entire cannula shield device is removed if a larger cannula length is required for introduction into a medicament bottle. There is neither a sealing means for the syringe content nor the possibility of verifying premature manipulations at the syringe; rather is it possible without any difficulty to remove and reposition the entire cannula shield means, or at least the front cap, without being able to notice it later on.
Finally, an injection syringe having a needle shield cap is known from WO-A-88/00478, in which the cap portion proper is integrally connected, via a predetermined breaking point, with a base portion intended for attachment. The known needle shield cap is closed on its front side and is provided for a disposable syringe assembly in which a disc-shaped seal is provided on the front-side end of the syringe body itself. Therefore, when using the syringe, at first this sealing disc must be pierced through by axially displacing the cannula rearwardly, for which purpose kind of a spindle drive is provided. Such a configuration is extremely expensive and disadvantageous in terms of manufacture and assembly of the cannula module and of the entire injection syringe. Moreover, it is disadvantageous that, when setting the syringe into operation, the cap portion is allowed to be rotated relative to the base portion and to the syringe body only in one specific sense of rotation to rearwardly displace the cannula for piercing through the sealing disc after having separated the predetermined breaking point. If the cap portion erroneously is rotated in the wrong direction, it may happen that the cannula is moved too much forwardly and the syringe becomes unusable. In addition, the cannula holding means requires a particularly great length, since it must be equipped with a rotational locking means relative to the cannula shield device on its forward end. The cannula itself likewise must be particularly long and must be ground on its two ends. The double-ground cannula is cast in the cannula holding means, which involves complex manufacturing procedures. Piercing through the sealing disc may result in the separation of particles getting then into the vaccine. Consequently, partial or total obstruction of the cannula may occur. A further disadvantage of the known construction is to be seen in that considerable pressure may build up within the vaccine, e.g., due to temperature fluctuations, which may cause the vaccine to leave the cannula immediately upon piercing through the sealing disc.